Serial ATA is an emerging disk connection standard, designed to replace the ATA connection inside standard personal computers (PCs). ATA is also known as Integrated Drive Electronics (IDE).
FIG. 1 shows a conventional connection between a host 10 (e.g. PC, RAID controller or disk drive controller) and a Serial ATA disk drive 12. There are two serial data paths, one sending commands and data from the host to the drive (transmit path 14), and one sending commands and data in the reverse direction (receive path 16). Each data path comprises a differential pair of signals.
It will be noted that if the host or disk controller 10 fails then it is not possible to access the data on the disk drive 12.
Unlike Fibre Channel disk drives, serial ATA drives do not have redundant ports as they only have one port to connect to the host or disk controller. Since there is only one port and since serial ATA connections are point to point links there is no option for redundant paths to the disk drive.
Some solutions to this problem include:                Making a Serial ATA disk drive with two ports; however, this requires an expensive customised disk with a non-standard connector; or        Mirroring the data on all Serial ATA disk drives so that there is a redundant path to the data rather than the disk; however, this requires twice the number of disk drives.        